1. Field of the Invention
This invention relates to a method of and an apparatus for electro-erosive machining. More specifically, it relates to a method of cutting a workpiece with an electrode in the form of a wire secured in at least one guiding head. Either the workpiece or the wire guiding head or both are at least initially oriented within a three-dimensional coordinate system. The apparatus for carrying out the method includes a wire guiding head in the form of a wire secured in at least one guide and a mechanism for orienting either the workpiece or the wire guiding head or both within a coordinate system.
2. Background of the Related Art
One particular problem encountered in optimizing the operation of an electro-erosive machine is idling. The machine may, for example, have to be kept idle for quite some time while it is set tip for a subsequent step or new procedure. Since shortening idling time reduces cost and improves exploitation, it is accordingly a constant objective in the development of electro-erosive machining. It is the initial orientation of the workpiece or wire electrode within the coordinate system that often requires keeping the machinery idle for a considerable time.
Orienting the wire electrode perpendicular to the surface of the workpiece (or in any other desired initial direction) is particularly difficult in cutting a workpiece. This operation takes considerable time and care at the current state of electro-erosive machining and requires relatively expensive arrangement for the wire positioning. One known approach involves designating at least one side of the workpieces as a reference surface and moving it to various X and Y coordinates at constant Z as established by comparator circuitry. When the workpiece is curved or thick, a reference point is usually bored into it to help locate it in the XY plane. In this event the workpiece is advanced until the bore arrives at a prescribed position.
The position of the reference surface of the workpiece in the XY plane is usually fine-adjusted with screws accommodated in a jig. Such a mechanism, however, can lead to deformation while he workpiece is being secured in it.
Positioning precision can also be detrimentally affected when the fine adjustment arrangement is inserted between the workpiece and the upper guide head. More room to maneuver than is needed while the workpiece is actually being cut out must accordingly be provided along the Z axis by raising the upper wire guide head farther off the surface of the workpiece. The longer Z-axis segment, however, also makes for even more potential errors and greater uncertainty in positioning the workpiece. Finally, each workpiece has to be positioned separately, even when several similar or different shapes are secured at the machining point.
How precisely the wire electrode itself can be oriented in relation to the workpiece depends on how precisely the workpiece is positioned on its supporting surface (usually about 3 .mu.m), how precisely any additional wire electrode-orientation mechanisms can be adjusted, and how precisely the contact between the wire electrode and the usually mutually perpendicular sides of the fine-adjustment mechanism can be defined. How the wire electrode comes into contact with the fine-adjustment mechanism is also extremely critical to these procedures because lateral force must be exerted on the wire electrode in order to fine-adjust it relative to the workpiece. This force occasions a difficult-to-handle lateral deflection and accordingly even more imprecision in the position of the wire electrode relative to the workpiece.